I'm having a chronic bug that I cannot replicate but I know it's a real thing. Asking for help.

I have a product that over the past couple years has become used by tens of thousands of people. I know that many of these people use the app just fine but recently I am getting more and more people emailing me saying

"I can't upload tracks"

I put this down to user error at first but it's becoming too common. I cannot replicate it. No-one I know can replicate it but it is 100% definitely a thing. My logs show this error:

Invalid argument supplied for foreach()

I'm at the end of my tether. I cannot understand why it works fine for almost everyone but for a few folk it absolutely doesn't. Also, it should be noted that it's not just a random bug - if you're one of the people this affects then it NEVER works for you.

Here's my code

JAVASCRIPT - This code powers a file upload widget that also handles the upload and passes the data to my controller so that I can store info in the database

<script src="//static.filestackapi.com/filestack-js/3.x.x/filestack.min.js"></script>

<script>
    // Set up the picker
    const clientOptions = {
        security: {
            policy: "{{$uploadpolicy}}",
            signature: "{{$uploadsignature}}"
        }
    }

    const client = filestack.init("{{env('FILESTACK_KEY')}}", clientOptions);

    const options = {
        storeTo: {
            location: 's3',
            path: '/audio/'
        },
        uploadConfig: {
            tags: {
                "app": "xxxxxxxx"
            }
        },
        onUploadDone: updateForm,
        maxSize: {{env('PRO_FILESIZE_LIMIT')}} * 1024 * 1024,
        maxFiles: {{env('PRO_TRACK_LIMIT')}},
        accept: 'audio/*',
        uploadInBackground: true,
        transformations: {},

        onFileSelected(file) {
            if (file.size > {{env('PRO_FILESIZE_LIMIT')}} * 1024 * 1024) {
                throw new Error('File too big, select something smaller than 240MB');
            }
        }
    };

    const picker = client.picker(options);


    const form = document.getElementById('pick-form');
    const fileInput = document.getElementById('fileupload');
    const btn = document.getElementById('picker');
    const nameBox = document.getElementById('nameBox');
    const urlBox = document.getElementById('urlBox');


    btn.addEventListener('click', function (e) {
        e.preventDefault();
        picker.open();
    });


    function updateForm(result) {
        $("#loading-wrapper").show();
        var data = result.filesUploaded;
        $.post({
            type: 'POST',
            url: '/uploadtrack/{{$artist_token}}',
            data: {uploads: result.filesUploaded},
            // dataType: 'JSON',
            success: function () {
                console.log("Aye thats them uploaded");
                location.reload();
            }
        });
    }
</script>

and this is my controller that catches the above and stores the data in the database

public function uploadtrack(Request $request, $token)
    {

        $artist = Artist::query()->where('token', $token)->first();
        $artist_token = $artist->token;
        $account_token = $artist->account_token;
        $user = Auth::user();
        $userID = $user->id;
        Log::info("TULOGS - START OF NEW - TRACK UPLOAD BY: ".$userID);

        $membertype = $user->membertype;
        Log::info("TULOGS - USER: ".$userID." MEMBERTYPE: ".$membertype);

        $trackcount = Track::countTracks($userID);
        Log::info("TULOGS - USER: ".$userID." TRACKCOUNT: ".$trackcount);
        Log::info("TULOGS - USER: ".$userID." / GOT MEMBERTYPE AND TRACKCOUNT");

        if ($membertype == "Free") {
            $tracklimit = env('FREE_TRACK_LIMIT');

            if ($trackcount >= $tracklimit) {
                dd("Track limit reached, please upgrade");
            }
        }

        if ($membertype == "Hobby") {
            $tracklimit = env('HOBBY_TRACK_LIMIT');

            if ($trackcount >= $tracklimit) {
                dd("Track limit reached, please upgrade");
            }
        }


        Log::info("TULOGS - USER: ".$userID." / GOT THROUGH THE IF STATEMENTS");
        Log::debug("The request: ".$request);

// All the uploads that fail log out "no" from the following little test:
        if ($request->uploads) {
            Log::debug("Yes");
        } else {
            Log::debug("No");
        }

// this is where it's failing. for the ones that don't work $request->upload is not a thing - BUT WHY?!
        foreach ($request->uploads as $upload) {
            $filename = preg_replace('/\.[^.\s]{3,4}$/', '', $upload['filename']);
            $track = Track::create([
                'user_id' => $userID,
                'track' => $filename,
                'artist_token' => $artist_token,
                'account_token' => $account_token,
                'filesize' => $upload['size'],
                'tracksource' => $upload['url'],
                'count' => 0,
                'token' => uniqid($userID, true).uniqid(),
                'key' => $upload['key'],
            ]);
            $newtracks[] = $track;
            ProcessTrackWaveform::dispatch($track);
            Log::info("TULOGS - USER: ".$userID." / ".$track);

        }

        Log::info("TULOGS - USER: ".$userID." / GOT THROUGH THE FOREACH");

        session(['data' => $newtracks]);

        Log::info("TULOGS - USER: ".$userID." / STORED THE SESSION DATA");

        return 200;

    }

Apologies for the excessive use of Logs - I'm trying to debug this.